Let's first talk about the following two sentences:
1- Sara went to bed as soon as she had finished homework.
2- Sara went to bed as soon as she finished homework.
I think your confusion is valid because we use the past perfect when we talk about something that took place before another thing in the past. So the use of the past perfect comes across in the first sentence but the use of the past simple in the second sentence doesn't. Am I right? In fact, we don't need to use the past perfect unless it is necessary or unavoidable to do so. Even if we talk about one action happening before the other one, it is possible to use the simple past for both actions if we think it is not necessary to highlight or emphasize the happening of the earlier action. It sounds natural to avoid using the past perfect where the simple past works, which is used to refer to something or several things happening in sequence (one after another) in the past.
So both of the sentences are grammatically correct. However, I'll prefer the second phrase to the first one.
As for the last two sentences, it is correct to say that "everyone had gone home when Sara got to the party", but it's not grammatically correct to say that "everyone had gone home when Sara had got to the party". It doesn't make sense. In the past perfect when we talk about two events, we use the simple past in one clause and the past perfect in the second clause.
Let's now talk about the following sentence you are confused about:
"Everyone went home when Sara had got to the party".
There is nothing wrong with this sentence, but the meaning is other way round. It means that first Sara got to the party and then every one went home. Look at the
first sentence again. When Sara got to the party, everyone had gone home. Here it means that first everyone went home and then Sara got to the party. Sometimes, one action happens soon after the other action, here we should use the past simple in both clauses such as when Sara got to the party, everyone left, when they saw the police, they ran away, etc.
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He went out five minutes ago - is definitely better than using "has gone".
You can also say:
He stepped out five minutes ago. - if you know that this person is coming back soon
or
He left 5 minutes ago.
Best Answer
Although I don't see any grammatical misuse in either sentence, in common usage I think most people would just say "I just got back from a friend's house." Since you just got back from that house, there is no need to specify that you had previously gone to it.
If you say "I had gone over to a friend's house.", it sounds as if you are relating it as an event previous to something else that you will also talk about; "I had gone over to a friend's house, and he got a phone call telling him his sister had been in an accident." It's also grammatically correct to use the other construction here: "I went over to a friend's house, and he got a phone call...". But using "had gone over" without something else sounds strange.